Update regarding the coins. And I kind of noticed this myself but didn't realize it until someone pointed it out.
There are at least 1 'special scenes' which give out a few extra clues, dispersed through the game. The more coins you have, the more scenes you see. For instance, on my first play through, I did not see a scene where
but I did see it on the 100% playthrough. This may be my bad memory, or the purpose of the coins.